Abstract On November 8th, 2018, the Camp Fire erupted in Northern California's Butte County. It was the deadliest and most devastating wildfire in California history, with over 153,336 acres burned, 86 confirmed fatalities, over 18,500 structures destroyed including nearly 14,000 residences. Over 50,000 people were evacuated. This fire was unusual not only in its scale and the rapidity of its spread to urban areas, but also in the vast area blanketed in smoke that followed for a defined window of two weeks until the first rainfall. The wildfire smoke plume spread quickly across vast areas of Northern California, and the air quality index was at hazardous levels for most of Northern California for two weeks, with particulate matter <2.5 m (PM2.5) concentrations reaching the highest levels ever recorded in the region, including large metropolitan areas like Sacramento, Oakland, San Francisco, and San Jose, affecting millions, including ~100,000 pregnant women. There are widespread concerns about potential health impacts of these urban wildfires and how to mitigate their effects, especially in vulnerable populations like pregnant women and their developing children. Exposure to extremely unhealthy levels of wildfire PM2.5 for nearly two weeks for the majority who were unable to leave Northern California are compounded by the unique composition of urban wildfire smoke. An array of potentially toxic volatile organic compounds may be released with high temperature combustion of chemicals widely used in building construction and interior furnishings, such as solvents, glues, metals, formaldehydes, and halogens. Additionally, like other disasters that act as inherently unpredictable forces of nature that threaten person and property, wildfires can induce emotional and psychosocial distress and potentially long-term consequences like persistent post-traumatic stress symptoms and depression. Exposures to contaminants and stress in combination could have serious long-term developmental consequences if delivered during critical periods in pregnancy. The goal of this R21 is to rapidly establish a cohort of women who were at different stages of pregnancy during the Camp Fire and their children, collect biosamples and survey information that will be used in future studies to determine exposure loads, mechanistic responses, health biomarkers and developmental outcomes. The cohort will have two eligibility arms: a) those residing within our target area closest to the fire and within a feasible driving distance for in-person pregnancy, delivery, and postnatal visits and future follow- up and b) women in Northern California pregnant during the Camp Fire who will complete an online survey and mail in biospecimens. Participant near-surface wildfire PM2.5 exposure estimated from satellite and ground monitor data, potential exposure-reducing behaviors, and residence aspects will be examined in relation to maternal symptoms, stress biomarkers, and child gestational age and birthweight. The cohort and biorepository established through this proposal will support future studies to understand and minimize the developmental effects of future wildfires, as they increase in number, duration, and intensity.